The effect of time of S application on yield and sulphur uptake of canola

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Abstract
Little information was available on the yield response of canola species to application of sulphur (S) fertilizer at various times after seeding. Split plot experiments having two cultivars, ‘Candle’ (Brassica campestris L.) and ‘Regent’ (Brassica napus L.) as main plots and four times of applying S fertilizer as subplots after seeding (0, 14, 28 and 42 days) were set out on six sulphur deficient soil sites of northern Saskatchewan. Sodium sulphate fertilizer was applied at 25 kg S/ha and all plots received 100, 20 and 50 kg/ha of N, P and K, respectively. The cultivar ‘Regent’ yielded 1.24 t/ha which was significantly higher than ‘Candle’ yielding 0.98 t/ha (average over sites). An estimated linear reduction in yield of canola grain of 0.11 t/ha for ‘Candle’ and 0.40 t/ha for ‘Regent’ was obtained with S applied at 42 days after seeding date. This difference in response to time of S application resulted in a cultivar x time of S interaction. On two other sites testing high in S (above 40 kg S/ha) there was an apparent increase in grain yield with S application at the rosette stage and at the second application time (12 days before reseeding because of frost damage). Sulphur uptake in grain and straw was highly correlated with yield of grain and straw. Average uptake of S in straw (15.1 kg S/ha) was higher than in grain (4.4 kg S/ha). With few exceptions, yield and S uptake in grain and straw was less with S fertilizer applied at late stages of growth than at seeding.